In order to solve the problems when conventional ground vehicles and wheels driving on soft terrain, such as poor trafficability，low efficiency， and big energy consumption, the transformable wheel was innovatively designed. Its design consisted of deformation mechanism, driving mechanism and wheel feet. The wheel had two extreme working statuses: unfolded wheel and folded wheel. It can realize walking and rolling. Based on classical terramechanics theory，the dynamics models of interactions between two types of working wheel status and three kinds of typical soft soils were established. Drawbar pull, driving torque and driving efficiency as well as sinkage of diametervariable wheel were analyzed under the condition of different slips, where the drawbar pull and driving torque were increased with the increase of slip rate, drawbar pull and drive torque of the unfolded wheel were up to 3990N and 2395N·m, and those of the folded wheel were up to 1435N and 1390N·m, respectively. In a certain radius of the wheel, the traction efficiency was soared to the maximum with the increase of slip rate and then it was slowly descended to zero. The maximum traction efficiency of unfolded wheel and folded wheel were 0.53 and 0.19, respectively, and the corresponding slip rate ranges were 0.1~0.2 and 0.2~0.3. The results indicated that traction trafficability indexes were limited by wheel slip and soft soil parameters．The unfold wheel can significantly improve drawbar pull，driving efficiency and soft soil traction trafficability，and reduce sinkage compared with the folded wheel. Finally, transformable wheel prototype trial production was presented, and installed on the amphibious allterrain vehicle by using the principle of submergingfloating. With the traction test, the unfolded wheel did not provide sufficient driving force when the slip rate was greater than 0.52 (that for folded wheel was 0.44), and the data was recorded six times. The difference between test results and computed results was less than 10%, which proved the applicability and validity of deformable wheel on soft terrain. 